Atheros extended Range XR Technology

Transcription

1 White Paper Atheros extended Range XR Technology Going the Distance

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3 Atheros extended Range XR Technology Executive Summary Wireless networking applications and services require an infrastructure that enables high bandwidth performance, ubiquitous coverage and robust delivery capability for WLAN products. While each market segment may have different application drivers and needs, all require these underlying infrastructure performance characteristics. As outlined in the Atheros white paper, Super G - Maximizing Wireless Performance, WLAN infrastructure performance requirements fall into two key areas that determine the quality of a wireless solution: Throughput- needed for bandwidth intensive applications and growing volume of users; must meet or exceed wired speeds Coverage-required for connectivity at long range and in all corners of the home, office, enterprise, or hot spot Adequate coverage is especially critical in the home/soho arena. Consumer product return decisions are frequently tied to the connection success or failure at the moment of installation. This means that ample range is crucial along with solving the wireless dead spot challenge. Of course, these requirements must also be addressed in a way that is easy for the user and/or network administrator to utilize and support. Atheros' extended Range (XR ) technology was designed to provide unprecedented wireless LAN coverage including: Line-of-sight range that is 2x to 3x that of traditional solutions: a connection where otherwise it is not possible Elimination of indoor dead spots Transparent operation with no user intervention required Enabled devices that still remain standards-interoperable with 3rd party devices 2004 by Atheros Communications, Inc. All rights reserved. April

4 extended Range technology consists of a signal processing architecture that stretches the performance of a WLAN by embedding separate optimized designs for both high performance/high signal-to-noise ratio environments and long range/low signal-tonoise ratio environments. XR is able to maintain standards compliance while providing these unique benefits individually to those stations and APs on a given network that can support this technology. Table 1-1 summarizes XR's components and benefits, which are described in detail later in this white paper. Table 1-1. extended Range Component Summary Component Benefit Enhanced Receive Sensitivity Up to 105dBm: over 20 db better than the specification Process extremely weak signals Supports additional transmission rates equivalent to 3, 2, 1, 0.5, 0.25 Mbps Extends support for signal beyond traditional boundaries Seamless Standard and XR Mode Support Transparent to users Standards-interoperable NOTE: Actual operational rates subject to specific regulatory requirements. Coverage Needs of Wireless Networking Applications Coverage is an issue for all segments as shown in figure 1-1. Traditional solutions were not designed to support many of the current coverage needs as follows: Home Typically, a single AP/router provides access to valuable broadband services and coordinates network activity throughout the home and yard. For a solid home network foundation, the following must be considered: A single AP must cover the entire property Pulling Ethernet cable for additional APs is not viable Placement of the AP may not be centrally located because it is dictated by the location of the broadband modem The WLAN must support transmission through all types of home layouts Many homes include basements with cement walls or converted garages Large variety of construction materials: stucco, brick, plaster, wood Emerging multimedia applications such as wireless audio players which are much less forgiving of dead spots must be supported 4 April by Atheros Communications, Inc. All rights reserved.1-4

5 Office Office environments are also susceptible to dead spots. The current solution is to deploy additional APs which is a costly installation and configuration exercise. Initial AP deployment with broader coverage is preferred in these scenarios due to configuration management simplicity and reduced cost. Public Areas Simply put, best possible range for public areas or hot spots translates to more users/customers capable of accessing the network and greater utility derived from the network. In summary, all market segments are experiencing coverage issues. Needs in All Segments For Homes: Single-AP Coverage Constant connection Place the AP anywhere Eliminate support calls Eliminate returns For Offices: Eliminates Dead Spots Reduce installation and configuration costs For Public Access: Cover Larger Areas Hotspots more users Figure 1-1. Coverage Requirements per Segment Resulting Coverage Requirements Common to Segments Extended Range Whether it's access from the yard, corporate conference room, or hot spot park bench, connectivity is critical. So, the WLAN architecture must be tuned for long range, low signal-to-noise environments as well as be able to support maximum throughputs in typical environments Reliable Coverage No dead spots - Given the desire for ubiquitous wireless networking, it must be deployed virtually everywhere without regard to specific construction materials. The attenuation characteristics of these construction materials varies greatly and wireless solutions must be robust enough to address these variabilities Ease of Use Like throughput enhancements, coverage enhancements must allow standard devices to maintain communication while enhanced stations and APs take advantage of the additional capabilities 2004 by Atheros Communications, Inc. All rights reserved. April

6 extended Range: Addresses Coverage Requirements XR Overview Atheros' extended Range (XR) technology is a method of processing signals that enables wireless networks to have fewer dead spots and greater range than typical products; in effect, a low gear for wireless networks. The basic methods of processing wireless signals, as defined by the IEEE a and g standards are optimized for the delivery of signals in environments where signal strength is strong. As range increases or walls intervene, signal strength drops, but the same basic signal processing methods are used. This is why dead spots occur in wireless networks and why the connection drops abruptly at longer ranges. extended Range products dynamically adapt to sub-optimal environments and process weaker signals more effectively. The products shift from the more limited signal recovery techniques described by the IEEE standard to more advanced techniques used in cellular and other wireless industries. As a result, extended Range (XR) greatly increases the coverage of an a/b/g network. Figure 1-2. extended Range Mode vs. Standard Mode In standard a/b/g mode (inner circle of Figure 1-2), Atheros' RF transmit power and high receive sensitivity capabilities translate to industry best range and throughput performance. However, there are situations where users require coverage beyond traditional capabilities and in areas where the AP signal may be weak due to propagation issues (outer circle of Figure 1-2). Key components of the XR solution include (1) Enhanced Receive Sensitivity and (2) Seamless Standard and XR Mode Support. 6 April by Atheros Communications, Inc. All rights reserved.1-6

7 XR Key Components 1. Enhanced Receive Sensitivity Received signal power falls rapidly with distance and obstructions which is a phenomenon called path loss. The capability to enable low signal to noise (SNR) operation is critical to address this RF signal path loss in all operating environments. Different environments experience varying effects of path loss. Further, indoor path loss is much worse than outdoor path loss due to greater attenuation of dense walls and objects. A common model for calculating 2.4 GHz RF path loss is as follows: Path loss(db) = P(1) + 10*log[D n ] where D = distance in meters (1 meter = 3.28 feet) P(1) = path loss at 1 meter = 41 db n = path loss exponent: open space = 2, open office = 3.3, home = 4.5 (Note that the path loss exponent varies based on attenuation characteristics of the specific environment) Home Case Study - Receive Sensitivity Using this model, we can estimate path loss for between 10 meters and 70 meters in a home environment at 10 meter increments. Of course, these figures can vary significantly depending on the environmental factors listed above. This exercise simply illustrates the importance of receive sensitivity differences. Table 1-2. Home path loss at 10 m increments 10 m 20 m 30 m 40 m 50 m 60 m 70 m Overall Loss 86 db 100 db 107 db 113 db 117 db 121 db 124 db Incremental Loss for Prior 10 meters N/A 14 db 7 db 6 db 4 db 4 db 3 db Two facts stand out: 1. As a station moves further away from the AP, each single db loss is more critical with respect to supported range. Further, this is magnified for an outdoor line-ofsight environment because a small difference in receive sensitivity can alter coverage by hundreds of meters. 2. As additional obstacles are introduced, the importance of each db is even more significant when coverage of a particular area is desired. For example, a ¾ piece of plywood can attenuate a signal by ~4dB, while a concrete wall can attenuate a signal on the order of ~8 15 db depending on thickness. So, when covering a structure at distances of ~30 meters or more through multiple walls or open air at much longer distances, it is essential to have very robust receive sensitivity capability to make practical use of weaker signals. Atheros has enhanced its MAC and PHY technology to support very low signal to noise (SNR) operation. This leads to significantly improved receive sensitivity measurements that provide superior signal processing capability. extended Range builds upon a/g by adding transmission rates equivalent to 3, 2, 1, 0.5 and 0.25 Mbps. As with typical operation, these new rates are added to the list of rates used by Atheros' rate adaptation algorithm to maximize throughput while maintaining reliable data transmission. This rate adaption automatically engages as required to mitigate the effects of distance, obstacles and interference by Atheros Communications, Inc. All rights reserved. April

8 Table 1-3. extended Range Receive Sensitivity vs. Standard Data Rate Receive Sensitivity Incremental Range Benefit for Home and Office IEEE Spec 85 dbm N/A Atheros 6 Mbps a/g std. 93 dbm N/A Atheros 1 Mbps b std. 96 dbm N/A Atheros extended Range 101 dbm 30-42% more range vs. 1 Mbps b at 1 Mbps Atheros extended Range at 250Mbps 105 dbm 58-86% more range vs. 1 Mbps b % more range vs. 6 Mbps ag NOTE: Improvements are even greater over 54 Mbps ag data rate. The obvious result of these receive sensitivity enhancements is the radically increased range as described in Table 1-3. Range benefits of a 9 db receive sensitivity (or SNR gain) advantage over a 1Mbps b solution can be derived as follows: 9dB/3.3 = n = 1.86 (where n = 2.7/10) 1.86 = 86% more range for office 9dB/4.5 = n = 1.58 (where n = 2.0/10) 1.58 = 58% more range for home (Note that 3.3 and 4.5 are the path loss exponents for open office and home, respectively.) Outdoor: Open Air The benefit is even more dramatic for the higher ag link rates and open air environments where XR range benefits are 2x to 3x. As shown in Figure 1-3, when compared to traditional g solutions in a simple line-of-sight test, XR clearly is superior with more than double the range. Figure 1-3. XR Superior Range 8 April by Atheros Communications, Inc. All rights reserved.1-8

9 2. Seamless Standard and XR Mode Support XR capable access points can communicate simultaneously with both legacy (non-xr) and XR-enabled stations, allowing XR stations to seamlessly roam between the standard and extended Range operations. This action is triggered by signal strength and link rate when both AP and stations are extended Range-enabled. As part of normal roaming operation, a station typically looks for other APs whenever its link rate with the current AP falls below an acceptable minimum. At that point, the station scans for other APs. This is done to enhance performance, increase channel capacity, support mobility via roaming to another AP, or simply maintain connectivity. XR fits seamlessly into this same roaming architecture. The XR capable stations will associate with XR capable APs as necessary to maintain a reliable connection. Practical Benefits for Home and Office extended Range technology is fully interoperable with other a, b, and g products. This feature operates transparently to the user, the network, and the operating system. An XR capable AP or station can communicate on a link-by-link basis with both products that support XR as well as with Wi-Fi compliant solutions. The XR benefits are enjoyed when communication is between an XR capable AP and an XR capable station. Figure 1-4 illustrates the XR benefits in a typical enterprise environment. While isolated rooms and corners are not served by traditional AP coverage, XR can provide coverage where an additional AP would otherwise need to be installed. XR reduces costly installations and minimizes overall configuration burden. AP Coverage b a/g with XR AP extended Range penetrates heavy duty walls Figure 1-4. Enterprise Environment Benefits 2004 by Atheros Communications, Inc. All rights reserved. April

10 Further, Figure 1-5 and Figure 1-6 illustrate the powerful impact of XR in a home environment. XR enables a single access point to cover a multi-story brick or masonry home and eliminate dead spots. This directly addresses key problems currently faced by WLAN solutions providers such as product support calls, product returns, and operational complexity. Place devices without regard for structural, distance or other potential obstructions Gives end-users freedom to enjoy wireless connectivity anywhere on the premises from the basement to the bedroom to poolside at the far end of the property Figure 1-5. Total-home-coverage Throughput a range limited by 6 Mbps link rate Extended Range transmission rates of 3, 2, 1, 0.5, and 0.25 Mbps dramatically increase range Range b a g a/g XR Figure 1-6. XR: Superior Range vs. Traditional April by Atheros Communications, Inc. All rights reserved.1-10

11 Conclusion Atheros' extended Range technology significantly benefits home users by allowing them to cover large, multi-story homes with a single access point (AP) or gateway. Moreover, home users can easily set up a wireless AP where the broadband connection enters the home, not just where it's optimal for radio signals to propagate. The number one reason for returned wireless products is lack of coverage or range, and for most customers XR is the solution to this problem. Its design allows individual stations and AP's to take advantage of XR technology on a link-by-link basis, even in mixed networks with third party devices. In an enterprise environment, XR improves wireless coverage by eliminating dead spots while at the same time allowing IT managers to invest in fewer access points. In outdoor environments, XR enables more economical point-to-point fixed wireless systems and provides for greater utility of public hot spot infrastructure with increased numbers of users able to connect to each access point. extended Range is the premiere extended coverage solution: 3x range of standard WLAN technologies in outdoor wireless networks Extends the reach of public hot spots 2x range of standard WLAN technologies in indoor wireless networks: Processes weak signals through walls Eliminates dead spots Allows placement of AP anywhere in home or office Provides reliable connection from the moment of initial deployment Reduces AP deployment costs in office environments Fully interoperable with a, b, g, and third party products No added configuration required by end-users Atheros extended Range technology is fully compatible with IEEE and Wi-Fi Alliance standards and will evolve as part of the Atheros technology suite by Atheros Communications, Inc. All rights reserved. April

12 The information in this document has been carefully reviewed and is believed to be accurate. Nonetheless, this document is subject to change without notice. Atheros assumes no responsibility for any inaccuracies that may be contained in this document, and makes no commitment to update or to keep current the contained information, or to notify a person or organization of any updates. Atheros reserves the right to make changes, at any time, to improve reliability, function or design and to attempt to supply the best product possible. Atheros and the Atheros logo are registered trademarks of Atheros Communication, Inc. All other trademarks mentioned in this document are the property of their respective owners. Document Number: Atheros Communications Incorporated 529 Almanor Avenue Sunnyvale, CA t: 408/ f: 408/ Subject to Change without Notice